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i June 21, 1993 =-N-m ffMA ARCO Service Station No. 0548, Stockton, California Working To Restore Nature • indicates that the sample collected from well MW-3 contains concentrations of non-fuel hydrocarbons. TOG was below laboratory detection limits in the ground-water sample collected from well MW-5. TPHg and benzene concentrations are shown on Plate 2. WORK IN PROGRESS We are currently preparing a work plan to install a vapor-extraction well adjacent to the area where the unauthorized leak occurred. This well will be incorporated into the vapor- extraction system which will be installed at the site in the future. CONCLUSIONS AND RECOMMENDATIONS The ground-water flow direction has consistently been southeast since October 1991. Dissolved gasoline hydrocarbons were detected in groundwater samples collected from monitoring wells MW-2, MW-3, and MW-5. RESNA recommends continued quarterly monitoring is warranted. We understand that Emcon will conduct the next quarterly monitoring event in June 1993. We recommend additional analyses be run on next quarters ground-water samples in order to identify non-fuel hydrocarbons and lower boiling point hydrocarbons. Because hydrocarbons were detected in soil samples collected in borings near the pump island area at depths near the capillary fringe and were probably transported by the ground- water surface, we recommend no further soil assessment in this area. Because TOG was not detected in the soil samples collected from borings B-lb and B-17 near the waste-oil tank, we recommend that no further soil assessment for TOG is warranted in this area. • We recommend that copies of this report be forwarded to Ms. Mary F. Meays of the San Joaquin Public Health Services, P.O. Box 2009, Stockton, California 95241 and Ms. Elizabeth Thayer of the Central Valley Regional Water Quality Control Board, 3443 Routier Road, Sacramento, California 95827-3098. • • • 0 0331ccar 30004-a 4 •